I'm sure each school will have different "rules." I only had 1 MMI interview, I think it was 8 stations, you had 2 minutes between each station to read the scenario outside the room, and 8 minutes inside the room to talk about your response to the scenario. You can just go in and start talking about your response.
For the acting interviews, you have VERY little time, so offering to get the SP a drink of water might be a kind gesture, but you don't want to waste time on that (plus you normally don't do that when interviewing patients/doing physicals anyway). Not sure why you are wondering about personal contact...do you mean like shaking their hand? If the scenario warrants it, sure. My acting scenario was with a woman who was playing my cousin, so shaking her hand would have been awkward. If you are acting with an SP, yes you should shake their hand.